1. Field of the Invention
The present invention relates to stabilizers for spandex polymer which provide the polymer with improved resistance to discoloration induced by exposure to fumes and/or ultraviolet light. More particularly, the invention concerns sugars or sugar derivatives that not only provide such improved resistance but also provide improved heat-set efficiency to fibers made from the spandex polymer.
2. Description of the Prior Art
Spandex elastomeric fibers are made from long chain synthetic polymers comprised of at least 85% segmented polyurethanes. Many additives are known for stabilizing spandex polymers and fibers against discoloration. Antioxidants in the form of hindered phenols are well known and families of such compounds have been produced commercially under trade names such as "Cyanox" by American Cyanamid Co., "Irganox" by Ciba-Geigy Corp., "Wingstay" by Goodyear Chemical Co. "Santowhite" by Monsanto Co., "Ethanox" by Ethyl Corp. and the like. Additives for stabilization of the polymer against ultraviolet-light-induced degradation, such as "Tinuvin", are sold by Ciba-Geigy Corp. The addition of zinc oxide to stabilize spandex polymer against chlorine-induced degradation or discoloration is known from Martin, U.S. Pat. No. 4,340,527. Japanese Patent Application Publication 59-210970 discloses sucrose fatty acid esters as stabilizers for polyurethane compositions. Saitoh et al, U.S. Pat. No. 4,499,221 discloses sucrose monolaurate as an optional additive to enhance the effect of a polymeric amine stabilizer in a polyurethane composition and further notes at column 6, lines 30 ff, that the composition "may further comprise any other conventional additive(s) such as inorganic fine powders (e.g., barium sulfate, titanium dioxide, silicates, zinc oxide, zinc sulfide), . . . ".
The above-described stabilizers have been useful in improving the resistance of polyurethane polymers against discoloration induced by heat, ultraviolet light, fumes, chlorine and the like. However, we have found that other problems are encountered when sugar fatty acid esters are used in preparing dry-spun spandex fibers or in finishing and heat-treating fabrics containing such fibers. For example, when sucrose monolaurate is used as an additive, the spandex fibers discolor unacceptably when they are incorporated into a fabric which subsequently is subjected to a conventional heat setting treatment at a temperature between 150.degree. and 200.degree. C.
It is an object of this invention to improve the utility of spandex polymer by enhancing its stability with additives that do not cause significant detrimental effect on its other physical properties or on its spinning and finishing characteristics when the polymer is converted into fiber.